1. Field of the Invention
The invention relates to data synchronization, and more particularly to multimedia data synchronization method and system utilizing additional information.
2. Description of the Related Art
NICAM (Near Instantaneous Companded Audio Multiplex), an audio multiplex system developed by the BBC, is used in PAL/SECAM TV broadcasting in Europe and Asia. A general NICAM frame starts with an 8-bit “Frame Alignment Word” (FAW), followed by five control bits, eleven bits of unprotected (no parity) additional data, and 704 bits of parity checked data, represented as:
FAWControlAdditional DataData(8 bits)(5 bits)(11 bits)(704 bits)
Five control bits (C0, C1, C2, C3, C4) are provided in each NICAM frame. The first bit C0 is a frame flag used for synchronization of NICAM frames, identifying the odd (C0=1) and even (C0=0) frames. The next three bits C1, C2, and C3 are used to specify the mode of transmission. Table 1 shows the relationship between the mode of operation and the bits C1, C2 and C3. The fifth control bit C4, a reserve sound switching flag, notifies the receiver if NICAM is lost. The receiver can then switch to the frequency modulation (FM) mono sound signal.
TABLE 1C1C2C3Mode of operation000One digital stereo channel010Two different mono channels (M1 and M2)100One 44K data channel and one mono sound channel110One 88K data channel (704 Kbit/sec)
FIG. 1 is a flowchart of a NICAM bitstream processing method. When a NICAM bitstream is input, differential quaternary phase-shift keying (DQPSK) demodulation is first performed (step S11) to determine whether NICAM frames are synchronized (step S12). If not, the NICAM frames are then synchronized (step S13), and the process proceeds to step S12. If the NICAM frames are synchronized in step S12, the NICAM frames are decoded to output the decoded NICAM bitstream (step S14).
Referring to FIG. 2, when the NICAM bitstream is received, it is determined whether a FAW with 0x4E is detected. When N FAWs with 0x4E are detected, decoding from the first frame begins. In the described process, however, a bitstream buffer is required to store input data for decoding from the first frame, decoding is not conducted in real time and false alarms may frequently occur. Thus, it is desired to have a method for fast and accurate synchronization.